pre {
  white-space: pre-wrap;
  padding-left: 2.5rem;
  counter-reset: step;
  counter-increment: step 0;
}

pre .line {
  position: relative;
}

pre .line:before {
  content: counter(step);
  counter-increment: step;
  position: absolute;
  left: -2rem;
  width: 1rem;
  margin-right: 1.5rem;
  display: inline-block;
  text-align: right;
  color: rgba(115,138,148,.4)
}

.error-squiggles-wrapper {
  position: absolute;
  width: 100%;
  height: 100%;
}

.error-squiggles {
  border-bottom: 2px dotted red;
}